They could potentially be introduced as a new threat. Maybe they find a way to cross over through some sort of interdimensional rift. The Sith's dark side powers would contrast greatly with the heroes in the MCU.
The MCU and comics have both similarities and differences. In some ways, the MCU brings comic characters and stories to life on the big screen very faithfully. But there are also changes made for cinematic purposes.
The MCU's ending in the comics is a combination of epic conflicts, unexpected plot twists, and resolutions that shape the future of the comic universe. It's a result of years of storytelling and character arcs coming to a head.
The MCU and Comic Earth 616 have very few direct connections. The MCU takes inspiration from various comic sources but creates its own unique universe and storylines that often differ significantly from those in Comic Earth 616.
The MCU often makes changes to characters' backstories and powers to better fit the cinematic universe. Some storylines are also simplified or adapted to work on the big screen.
Sure, the MCU does exist in the comics. The movies and TV shows draw inspiration from the extensive comic book universe. However, there are some differences and adaptations made for the screen to make the stories more accessible and engaging for a wider audience.
MCU Thor's appearance and costume design are distinct from the comics. The way his powers are visually depicted and the extent of their use can also differ. And the overall tone and style of the stories in which he appears in the MCU and comics can be quite different.